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A290473
Numbers k such that 3*10^k + 13 is prime.
0
1, 2, 4, 10, 12, 13, 26, 37, 56, 66, 288, 404, 3495, 3824, 7780, 14824, 17928, 18680, 21414, 23782, 25392, 34749, 36180, 46316, 48477, 63522, 73962, 89206, 139722, 172812, 184110
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 0 followed by the digits 13 is prime (see Example section).
a(32) > 2*10^5.
EXAMPLE
4 is in this sequence because 3*10^4 + 13 = 30013 is prime.
Initial terms and associated primes:
a(1) = 1, 43;
a(2) = 2, 313;
a(3) = 4, 30013;
a(4) = 10; 30000000013;
a(5) = 12, 3000000000013; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[3*10^# + 13] &]
PROG
(PARI) lista(nn) = for(n=1, nn, if(ispseudoprime(3*10^n + 13), print1(n, ", "))); \\ Altug Alkan, Aug 03 2017
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Aug 03 2017
EXTENSIONS
a(29)-a(31) from Robert Price, Jul 26 2018
STATUS
approved